Volatile liquid pumping system



Oct. 19, 1965 E. P. THOMAS ETAL 3,212,280

VOLATILE LIQUID PUMPING SYSTEM 5 Sheets-Sheet 1 Filed Nov. 22, 1965 Rmaf//Bf 1/ TTRNEX Oct. 19s 1965 E. P. THOMAS ETAL 3,212,280

VOLATILE LIQUID PUMPING SYSTEM Filed NOV. 22, 1965 Oct- 19, 1965 E. P. THOMAS ETAL 3,212,280

VOLATILE LIQUID PUMPING SYSTEM Filed Nov. 22 1963 5 Sheets-Sheet 5 panal/. SM

TTHNEY.

Oct. 19, 1965 E. P. THOMAS ETAL 3,212,280

VOLATILE LIQUID PUMPING SYSTEM 5 Sheets-Sheet 4 Filed Nov. 22, 1965 I INVENTORS, Edmund I? Toms Qel'fA 21749015' 2n .A/- 54M ATTORNEY OC- 19, 1965 E. P. THOMAS x-:TAL 3,212,280

VOLATILE LIQUID PUMPING SYSTEM Filed Nov 22, 1963 5 Sheets-Sheet 5 z' .Zd

United States Patent 3,212,280 VLATILE LIQUID PUMPING SYSTEM Edmund P. Thomas and Leif A. Ness, Bethlehem, Pa.,

assignors to Air Products and Chemicals, Inc., a corporation of Delaware Filed Nov. 22, 1963, Ser. No. 325,604 1S Claims. (Cl. 62-55) The present invention relates to apparatus for pumping highly volatile liquids such as, for example, liquid hydrogen, oxygen, nitrogen, carbon monoxide, argon, etc., and, more particularly, to a pumping system capable of pressurizing and discharging large volumes of highly volatile liquids at pressures in the range of 100 to 10,000 p.s.i.g. with substantially increased efiiciency.

In addition to the normal problems involved in the design of large volume pumping systems, special problems are present in the case of systems for pumping highly volatile materials such as cryogenic liquids and these include the problem of maintaining the temperature of the liquid in the range of minus 60 F. to minus 425 F. throughout its passage through the system as well as maintaining the pressure of the liquid substantially above the vapor pressure so that vaporization or flashing is prevented. The latter problem is of major significance in the case of positive displacement pumps wherein the pump chamber pressure is normally allowed to drop substantially below the inlet pressure during the suction stroke so that a net positive suction head (NPSH) is applied to the inlet check valve in order to open the valve. This type of operation is wholly undesirable when volatile liquids are being pumped since the reduction of pressure in the pump chamber permits the liquid therein to vaporize which either reduces the pump efficiency, since the vapor must be compressed, or completely vapor locks the pump so that no liquid is pumped, these alternative results being dependent upon the degree of pressure reduction occurring in the chamber.

It is therefore the general object of the present invention to provide a pumping system of greatly increased efficiency rand it is a more specific object of the present invention to provide .a pumping system wherein temperature and pressure control is substantially improved.

In brief, the present invention includes the provision of a plurality of pumps individually submerged in the pumped liquid and collectively surrounded by a cold gaseous atmosphere of either the material being pumped, as where such material is hydrogen or nitrogen, or an inert material such as nitrogen, when the material being pumped is liquid oxygen.

In addition, the present invention includes the provi- Sion of an improved cooperating relationship between the pump piston and the pump inlet valve whereby the latter is actuated by the former in a manner which prevents dashing of the liquid in the pump chamber.

In a preferred embodiment of the invention, a resilient interengaging connection of the detent type is provided between the inlet valve and the piston so as to result in a make-and-break or lost motion connection as the valve and the reciprocating piston move along their respective paths of travel, such paths preferably being along a common, longitudinally extended axis or on parallel axes.

The above object as well as other relating more particularly to the details of the system and the operation thereof will become more fully apparent from the following description when taken with the accompanying drawings, in which:

FIGURE l is a fragmentary sectional view of a three pump system contained within a single housing, the pump driving mechanism being omitted since it forms no part of the present invention;

FIGURE 2 is a sectional view taken along the plane indicated by line 2 2 of FIGURE 1;

FIGURE 3 is an elevational View of `an individual pump with portions thereof being shown in section for purposes of clarity;

FIGURE 4 is a sectional View taken along the plane indicated by line 4-4 of FIGURE 3;

FIGURE 5 is a fragmentary sectional View taken along the plane indicated by line 5-5 of FIGURE 4;

FIGURE 6 is a fragmentary top View of the right end portion of FIGURE 3;

FIGURE 7 is a fragmentary sectional view of an individual pump taken along the plane indicated by line 7-7 of FIGURE 3;

FIGURE 8 is a sectional view of the pump taken along the plane indicated by line 8-8 of FIGURE 7;

FIGURE 9 is a fragmentary sectional view showing the details of the piston and inlet valve structure of an individual pump, the pump elements being illustrated in the positions which they occupy at the beginning of the suction stroke;

FIGURE 10 is a fragmentary sectional view showing the same elements in the positions which they occupy during a later portion of the suction stroke;

FIGURE 11 is a fragmentary sectional view showing the same elements in the positions which they occupyv during a still later portion of the suction stroke;

FIGURE 12 is a fragmentary sectional view showing the same elements in the positions which they occupy during the later portion of the compression stroke; and

FIGURE 13 is a pressure versus volume diagram illustrating the operating characteristics of 'an individual pump.

Referring first to FIGURES 1 and 2, the pumping system includes a vertical, circular mounting plate 11 of sufficient strength and rigidity to support a plurality of pump units as well as the manifold and storage components of the system. An elongated, bell-shaped housing 12 is attached to the mounting plate 11, as by conventional lianged connection, to form a large chamber 13 containing yall the pumping and directly associated apparatus. Housing 12 is preferably of double-walled construction consisting of thin sheet-metal shells 14 spaced as shown and vacuum-packed with insulating material 15 which, for example, may consist of perlite.

The mounting plate 11 is faced on its inner surface with a thick layer 16 of insulating material such as polyurethane foam. A rst aperture is provided in mounting plate 11 to receive an inlet conduit generally indicated by numeral 17 through which the liquefied gas is supplied to the multiple pump assembly under a low pressure such as 30 p.s.i.g. In addition, plate 11 is provided with apertures through which there extend an outlet conduit 18 and valve controlled conduits 19 and 19' the latter of which permit the regulation of gaseous refrigerant within charnber 13 as will be described hereinafter in more complete detail.

In order to prevent a heat leak along conduits 17 and 18, these are preferably sealed with respect to plate 11 by means of O-rings which are held in grooves in plate 11 by annular rings 22 bolted or otherwise secured to the plate. In addition to the above-mentioned apertures, the central portion of mounting plate 11 is provided with three apertures equi-spaced along the horizontal diameter of the plate. Through these openings, as well as through aligned openings formed in the thick layer of rigid foam 16, extend cylindrical members 23 of rigid, strong insulating material, such as a laminated plastic. The rigid members 23 form the end supports for the individual pump units generally indicated by numeral 24a, 24h, and 24C.

In order to prevent heating of the pumped liquid externally of the pumps, conduits 17 and 18 are of doublewalled construction comprising inner, fluid-conducting pipes 17' and 18 and outer, thin sheet-metal shells 20 and 21, respectively; the shells being concentrically spaced about their respective pipes and vacuum insulated.

The central pipe 17 of inlet conduit 17 extends for some distance into the chamber 13 and is connected so as to discharge the liquefied gas into a common distributing manifold 26. From manifold 26 individual pump inlet conduits 27a, 27b, and 27C extend to locations adjacent the layer of vinsulation 16 and are there turned upward to enter the underside of the mounting blocks 28 of the respective pump units.

As will be subsequently described in detail, each pump unit is operative to pressurize the liquefied gas to a pressure in the range of 100 to 10,000 p.s.i.g. and the liquid is then discharged at this pressure through outlet conduits 29a, 29b, and 29C connected to the upper side of mounting blocks 28 diametrically opposite the inlet conduits 27a, 27b, and 27C. Outlet conduits 29a, 29b, and 29C extend upwardly and horizontally so as to connect with a common outlet manifold 31 from which the high pressure liquid discharges through pipe 18 and outlet conduit 18 to the place of intended storage or use, not shown.

Each of pump units 24a, 24h, and 24e is also connected through one of bleed conduits 32a, B2b, and 32e to a common, cylindrical tank 33 having a vent conduit 34 controlled by a valve 35. Valve 35 is of the normally closed type but may be manually opened upon movement of -handle 37 which is connected to the valve through actuating rod 36. Thus, valve 35 permits the venting of the gas which is produced upon boil-off of the liquid during the initial cool-down of the system as well as any vaporization which occurs thereafter as lwill be more fully described in the subsequent description of the operation.

Of course, the type of gaseous atmosphere to be maintained within chamber 13 will depend upon the nature of the liquefied gas 'being handled by the system. Where hydrogen is the liquid, the vapor from tank 33 is vented directly into chamber 13 to maintain low temperature conditions therein and may be withdrawn therefrom through one or both of previously mentioned conduits 19 and 19. The same procedure is employed when liquid nitrogen is being pumped. However, when liquid oxygen is being pumped, it is not desirable to vent oxygen into chamber 13 since oxygen is incompatible with the polyurethane foam 16. Therefore, vent conduit 34 is then provided with an extension beyond the valve 35 so as to convey the boiled-off oxgen outside the chamber 13, as by passing through the layer of insulation 16 and the mounting plate 11. With gaseous oxygen being piped directly from tank 33 to the exterior of chamber 13, the latter may be continuously purged with inert gas, such as nitrogen, -by introduction to and withdrawal from the chamber 13 through the small conduits 19 and 19.

Having described the over-all pumping system, :reference is now made to FIGURES 3 to 12 which illustrate the details of an individual pump unit 24a. Since all of pump units 24a, 2411, and 24e are identical in construction and operation, only one unit will be described in detail. Unit 24a includes an elongated, bell-shaped housing 45 having a tiange 46 which is secured by screws 47 to block 28 the latter of which `forms the base of the individual pump generally indicated by numeral 41. Pump 41 `further includes a main body portion 42 one end of which may be integral with or otherwise secured to base 28 and the other end of which is enlarged at 44 so as to contain the pump inlet and outlet valves which will be subsequently described in detail.

As shown most clearly in FIGURES 3 and 7, a continuous bore 38 extends through the pump base, main body portion 42 and terminates in an end portion 39. An elongated piston is received within bore 38 so as to reciprocate therein and it will be noted that the piston carries a plurality of piston rings 43 so as to be in sealed relationship with the bore. Of course, it will be readily understood that piston 40 is reciprocated by conventional means such as a slider crank drive mechanism (not illustrated) and that bore portion 39 -forms the actual pumping chamber for the workin g pump piston 40.

As most clearly shown in FIGURES 3 and 4, mounting block 28 of the pump unit is provided with a first bored passage 4S whereby pump inlet conduit 27a communicates with chamber 51 formed by housing 45. Block 28 further contains a second bored passage 49 communicating with pump outlet conduit 29a and a third bored passage 52 the latter of which places chamber 51 in communication with bleed conduit 32a as most clearly shown in FIGURE 5. Thus, the liquefied gas is introduced into chamber 51 through conduit 27a and passage 48 so as t0 completely fill the chamber. A minor portion of the liquefied gas flows through passage 52 and bleed conduit 32a to tank 33 while the major portion of the liquid in chamber 51 is drawn into pump 41 through the inlet valve structure which will now -be described with particular reference to FIGURES 7 and 9 to l2.

Enlarged portion 44 of the pump body includes a conical opening 50 which is aligned with bore 38 and which receives the conical portion 54 of a valve body 53, the external surface of portion 54 preferably being provided with a plurality of grooves for sealing purposes. Valve body 53 also includes an enlarged flange 5S having apertures through which there extend a plurality of stud bolts 56 secured at one end in body portion 44. Studs 56 extend beyond the outer face flange 55 and terminate in threaded end portions adapted to receive nuts 57, washers 5S, and spacer sleeves 59 whereby valve body 53 may be removably clamped in position to form the pump cylinder head.

As further shown in FIGURES 7 and 9 to 12, valve body 53 is provided with a plurality of bored passages 64 which lead from chamber 51 to an inlet manifold space 63 formed in conical portion 54. In addition, valve body 53 is centrally bored so as to receive the stern 60 of an inlet valve generally indicated by numeral 61. Valve 61 includes a disc-shaped head 62 which is biased toward seated engagement with the annular end surface of portion 54 by a compression spring 65 interposed between valve body 53 and abutment 66 secured to the valve stem. Of course, it will be noted that the diameter of valve head 62 is sufficiently less than the internal diameter of pump chamber 39 so that the liquid may flow around the perimeter of the valve head and into the pumping chamber at a rate consistent with the speed of the piston movement during the suction stroke.

The mechanism for positively controlling the opening movements of the inlet `valve will now be described with particular reference to FIGURES 7 and 9 to 12. This mechanism includes a spring clip 67 having a head portion secured by screw 68 in a recess formed in valve head 62. Spring clip 67 preferably includes a plurality of separate, axially extending fingers each of which is bent radially outwardly and then radially inwardly so as to form detent portions 69 which cooperate with the piston structure about to be described.

The head of pump piston 40 is provided with a shallow,`

clip 67 are radially compressed as they pass through the narrow portion of the bore formed by ridge 73. However, when detent portions 69 reach the groove 72, they radially expand to their normal position in which position there is a slight clearance between the detent portions and the walls of groove 72 as shown in FIGURE 9. Thus, the axial width of groove 72 permits a predetermined amount of back-lash or lost motion between piston 40 and valve 61 for the purpose hereinafter described.

The pump outlet valve structure will now be described With particular reference to FIGURES 7 through 1l. This structure includes a pair of tapered passages 74, which communicate with enlarged recesses 75 extending radially through pump body portion 44. Each tapered passage 74 receives an annular ring 76 preferably composed of a hard alloy which serves as a replaceable valve seat for an associated check valve 77T Each of check valves 77 is identical in construction and includes a body portion 78 threaded into recess 75, a disc-shaped valve head 79 connected to a valve stem 80 and a compression spring 81. Stern 80 is guided for longitudinal movement in a bore 82 in body 78 and spring 81 has suicient biasing force to maintain the valve closed so long as the pressure in the pump chamber does not substantially exceed the pressure on the discharge side of the valve in recess 75.

Referring now to FIGURES 3, 7, and 8, each of recesses 75 is in communication with an individual outlet passage 83 extending through pump body portion 44 and communicating with an associated outlet conduit S4 one end of which is suitably secured to portion 44. The opposite ends of parallel conduits 84 are connected to an arcuate manifold 85 which, in turn, is connected by -conduit S6 to previously-recited passage 49 leading to pump outlet conduit 29a.

Operation For purposes of describing the operation of the system, it will be assumed that liquid nitrogen is the fluid being pumped although it will be readily apparent that the system is equally well adapted to handle other volatile liquids including such fluids as superheated water wherein the problems of undesired vaporization and temperature control are also present. However, assuming that liquid nitrogen is to be pumped, the liquid nitrogen at a ternperature in the order of minus 320 F. is supplied from a source such as a storage vessel (not illustrated) under a low pressure such as 30 p.s.i.g. through inlet conduit 17, pipe 17', manifold 26, and each of individual inlet pump inlet conduits 27a, 27b, and 27C to chambers 51 of pump units 24a, 24b, and 24C. During the initial portion of the start-up period when the system components are relatively warm, a considerable amount of liquid nitrogen boils olic and this Vapor rises to the top of chambers 51 from which it ows through passage 52 and individual conduits 32a, 32h, and 32el to tank 33 from which it is vented through Valve 35 to the interior of chamber 13. Of course, this vapor is also extremely cold since the normal boiling point of nitrogen is minus 320 F. Thus, the continuous circulation of this vapor in chamber 13 and the withdrawal thereof through conduits 19 and 19 assists the rapid cooling of the components so that the cool-down period is substantially reduced.

Upon completion of the cool-down period, chambers 51 become completely lled with liquid nitrogen and the pumps may be started. Thus, the liquid nitrogen in charnbers S1 is pumped by the individual pumps 41 and discharged through check valves 77, passages 83, parallel conduits 84, manifolds 85, conduits 86, passages 49, and individual pump outlet conduit 29a, 29E, and 29e to manifold 31 from which the high pressure liquid nitrogen is supplied to the intended point of use through pipe 18 and outlet conduit 1S.

Having described the operation of the over-all system, reference is now made to the specic mode of operation 'of each of pumps 41 and, in particular, to the co-action of liquid nitrogen.

6 between pump piston 43 and inlet valve 61 as most clearly illustrated in FIGURES 7 through 13.

FIGURE 7 illustrates the pump elements in the positions which they occupy at the time corresponding to point 1 on the P-V diagram of FIGURE 13 at which time piston 40 has just completed a compression stroke. It will be noted that inlet valve head 62 is substantially fully received in recess 70 and that detent portions 69 of spring clip 67 are positioned in axial alignment with the internal end of groove 72. At this instant, outlet Valves 77 have just closed due to the biasing force of springs 86 and it will be understood that high pressure liquid nitrogen fills bore 71, the passages within rings 76, and the small space between piston 40 and rings 76 all of which collectively constitute the clearance volume designated C in FIGURE 13. Of course, inlet valve 61 is closed at this time due to the combined force of spring 65 and the high pressure liquid nitrogen trapped in b-ore 71 which is much greater than the lov. pressure liquid in inlet manifold chamber 63.

Reference is now made to FIGURE 9 wherein piston 40 is illustrated as being in the position which it occupies at the time corresponding to point 2 on the P-V diagram. At this early stage of the suction stroke, the piston has moved from the position illustrated in FIGURE 7 through a distance equal to the axial length of groove 72 so that detent portions 69 of spring clip 67 are in engagement with ridge 73. This movement increases the volume of the pump chamber by an amount designated E in FIG- URE 13 and produces a corresponding decrease in the pressure of the liquid which, although substantially incompressible does have some degree of compressibility. Of course, the degree of compressibility varies for diierent volatile liquids with liquid hydrogen having a relatively large degree of compressibility as compared to that Therefore, the volume E is predetermined to be sufliciently small so that the pressure of the liquid in the pumping chamber does not drop appreciably .below the pressure in inlet manifold chamber 63. Thus, the pressure in pumping chamber 39 remains substantially equal to the pressure in inlet chamber 63 which is well above the vapor pressure of the liquid. As a result, flashing or Vaporization of the liquid in the pump chamber is positively prevented. It will therefore be apparent that, at point 2 of the P-V diagram, there is substantially no pressure differential across valve head 62 and this valve remains closed due to the unopposed biasing force of spring 65.

At this point it should be noted that the movement of piston 40 just described is mechanically independent of valve 61 due to the back-lash or lost motion provided by the axial length of groove 72. However, as the piston continues the suction stroke, detent portions 69 are engaged by ridge 73 so that the piston effectively pulls the valve open against the light biasing force of spring 65. Spring 65 is progressively compressed until abutment 66 strikes valve body 53 at which point the valve is in the fully open position illustrated in FIGURE l0. Thereafter, continued movement of the piston causes radial compression of the spring clip so that the detent portions slip over the ridge thereby disconnecting the valve from the piston as illustrated in FIGURE 1l. Of course, this movement of the piston increase the volume of the pumping chamber so that the pressure therein drops slightly below the inlet pressure. As a result, the liquid tows around the edges of valve head 62 and the Velocity head of the liquid maintains the Valve in open position against the light biasing force of spring 65. At this point it is to be understood that spring 65 is selected so as to have a very low biasing force which, for example, may !be less than 0.5 pound of force. It will therefore be apparent that only a very small pressure differential is required across the valve head and, as a result, the pressure in the pump chamber is maintained Well above the vapor pressure throughout the suction stroke.

Immediately upon reaching the end of the suction stroke spring 65 assists the closing of valve 61 and the compression stroke is initiated with a consequent increase in pressure -as represented by the curve connecting points 3 and 4 on the P-V diagram, Of course, both the inlet and outlet valves remain closed until the predetermined pressure of point 4 is reached at which time check valves 77 open 'and the high pressure liquid nitrogen is discharged through the outlet conduits previously described.

As the compression stroke continues along the line between points 4 and 1 on the P-V diagram, the point is reached at which ridge 73 comes into engagement with detent portions 69 as illustrated in FIGURE l2. Continued movement of piston 43 toward the closed inlet valve causes the detent portions to radially contract thereby sliding over the Iridge .and nally protruding into bore 71 so that the detent portions are axially opposite the internal end of groove 72 as illustrated in FIGURE 7. Thus, one pumping cycle is completed and the elements are returned to their initial relative positions so as to repeat the above-described movements during succeeding cycles.

During continued operation of the pumps at relatively high speed, some undesirable heat is produced primarily as a result of the frictional engagement between the piston rings 43 and the walls of bores 38. However, as most clearly shown in FIGURES 3 and 7, the entire lengths of elongated pump portions 42 are in contact with the cryogenic liquid in chambers 51 so that the frictional heat is readily conducted through the pump walls to the liquid. This heat is rapidly dissipated by vaporizing a small amount of the liquid and the resultant vapor rises to the tops of chambers 51 from which it is vented through passages 52 and conduits 32a, 32b and 32C to tank 33 from which it may be periodically vented into chamber 13 through opening of valve 35.' Thus, in addition to removing undesired frictional heat, the present invention utilizes the vaporized gas to purge and cool the atmosphere surrounding the other components of the system.

From the foregoing description of the structure and operation it will be apparent that the present invention accomplishes the general objective of providing a pumping system particularly adapted for handling volatile liquids with substantially increased elliciency and that this beneficial result flows directly from the principles of the invention regarding the improved arrangement of components for minimum heat loss and the disclosed relationships between the pump elements. Therefore, since numerous variations and modifications will be readily apparent upon consideration of the above-disclosed principles, it is to be understood that the foregoing description is intended merely to illustrate one possible embodiment of the invention and that the latter is not to be limited other than as specifically set forth in the following claims.

What is claimed is:

1. A pump including means forming a pumping chamber, inlet and outlet valve means controlling iluid ow to and from said chamber, pumping means movable with respect to said chamber for compressing huid within said chamber, means mounting said inlet valve means and pumping means for mutually independent movement, and means for intermittently connecting said pumping means to said inlet valve means for actuating said inlet valve means in response to predetermined movements of said pumping means.

2. A pump including means forming a pumping chamber, inlet and outlet valve means controlling fluid flow to and from said chamber, pumping means movable with respect to said chamber for compressing fluid within said chamber, means mounting said inlet valve means and pumping means for mutually independent movement, and means for intermittently connecting said pumping means to said inlet valve means for opening said inlet valve means in response to the movement of said pumping means during the suction portion of the pumping cycle.

3. A positive displacement pump including means formsaid pumping member and said inlet valve for opening said inlet valve against the force of said biasing'means at a predetermined instant during the suction movement of said pumping member.

4. A liquid pump for pressurizing highly volatile liquids including means forming a pumping chamber, inlet and outlet valves controlling the flow of said liquid to and from said chamber, a pumping member mounted for suction and compression movements relative to said chamber, means mounting said inlet valve and pumping member for mutually independent movement, and means for intermittently interconnecting said pumping member and said inlet valve for positively opening said inlet valve during the suction movement of said member while the pressure in said chamber is substantially above the vapor pressure of said liquid.

5. A liquid pump for pressurizing highly volatile liquids including means forming a pumping chamber, inlet and outlet valves controlling the ow of said liquid to and from said chamber, a pumping member mounted for suction and compression movements relative to said chamber, means mounting said inlet valve and pumping member for mutually independent movement, and means for intermittently interconnecting said pumping member and said inlet valve for positively opening said inlet valve during the suction movement of said member while the pressure in said chamber is substantially equal to the inlet pressure and substantially above the vapor pressure of said liquid.

6. The pump as claimed in claim 1 wherein said means for intermittently connecting said inlet valve means and said pumping means includes rst and second frictionally engaging elements one of which elements is secured to said pumping means and the other of which elements is secured to said inlet valve means.

7.`The pump as claimed in claim 6 wherein said iirst and second elements are shaped so as to form a lost m0- tion connection whereby said pumping means moves a predetermined distance during the suction cycle before opening said inlet valve means.

8. The pump as claimed in claim 6 wherein one of said elements comprises a recess in said pumping means for receiving the other of said elements therein during at least a portion of the suction cycle.

9. In a liquid pumping system for pumping highly volatile liquids wherein the eiciency of said system is dependent upon the temperature and pressure of the pumped liquid, a liquid pump unit having an inlet and an outlet, insulation means forming an insulated chamber internally of said insulation means and surrounding said unit, means for venting vaporized liquid from said pump unit directly into said chamber for controlling the temperature surrounding said unit, and means within said pump unit for maintaining the pressure of the liquid substantially above the vapor pressure throughout the passage thereof between said inlet and outlet.

10. The liquid pumping system as claimed in claim 9 wherein said means for venting vaporized liquid into said chamber includes a selectively operable valve, and outlet' means for controlling the rate of discharge of said vaporized liquid from said chamber.

11. A liquid pumping system for pumping cryogenic liquids at low temperatures comprising at least one pump unit, said pump unit including a casing containing said cryogenic liquid and a pump at least partially submerged in said liquid, insulation means forming an insulated chamber internally of said insulation means and surroundingsaid pump unit, and means for venting vaporized and containing a cryogenic liquid to be pumped, said liquid directly into said chamber for maintaining a low temperature atmosphere surrounding said pump unit.

12. The liquid pumping system as claimed in claim 11 including a plurality of pump units Within said insulated chamber, and vent conduits connected to al1 of said pump units for venting vaporized liquid directly into said insulated chamber.

13. The liquid pumping system as claimed in claim 11 including a plurality of said pump units positioned within said insulated chamber, a single liquid inlet conduit and a single liquid outlet conduit extending externally of said chamber, and conduit means disposed entirely within said insulated chamber connecting all of said pump units to said single inlet and outlet conduits.

14. The pump as claimed in claim 1 in combination with means forming a rst chamber surrounding the pump and containing a cryogenic liquid to be pumped, said pump being at least partially submerged in said liquid, insulation means defining a second chamber internally of said insulation means surrounding said first chamber, and means for venting vaporized liquid from said rst chamber into said second chamber whereby an envelope of cold, vaporized liquid is maintained about the pump.

10 v 15. The pump as claimed in claim 6 in combination with means forming a first chamber surrounding the pump pump being at least partially submerged in said liquid, insulation means defining a second chamber internally of said insulation means surrounding said first chamber, and means for Venting vaporized liquid from said first chamber into said second chamber whereby an envelope of cold, vaporized liquid is maintained about the pump.

References Cited by the Examiner UNITED STATES PATENTS 2,831,325 4/58 White 103-153 X 2,837,898 6/58 Ahlstrand 103-178 2,855,859 10/58 Petzold 103-178 2,888,879 6/59 Gaarder 62--55 X 2,957,422 10/60 Loeber 103-40 3,000,319 9/61 Tuck 103-40 3,109,293 11/63 Williams et al. 62-55 3,147,877 9/64 Beckman 62-45 X FOREIGN PATENTS 1,223,190 1/60 France.

ROBERT A. OLEARY, Primary Examiner. 

1. A PUMP INCLUDING MEANS FORMING A PUMPING CHAMBER, INLET AND OUTLET VALVE MEANS CONTROLLING FLUID FLOW TO AND FROM SAID CHAMBER, PUMPING MEANS MOVABLE WITH RESPECT TO SAID CHAMBER FOR COMPRESSING FLUID WITHIN SAID CHAMBER, MEANS MOUNTING SAID INLET VALVE MEANS AND PUMPING MEANS FOR MUTUALLY INDEPENDENT MOVEMENT, AND MEANS FOR INTERMITTENTLY CONNECTING SAID PUMPING MEANS TO SAID INLET VALVE MEANS FOR ACTUATING SAID INLET VALVE MEANS IN RESPONSE TO PREDETERMINED MOVEMENTS OF SAID PUMPING MEANS. 